CD38/CD31 crosstalk promotes survival and proliferation of CD38⁺ B-CLL cells. Purified B-CLL cells from 4 patients (nos. 2, 4, 6, and 7) were cocultured with L-CD31⁺ or L-mock transfectants. After 3 days, B-CLL cell viability was determined by annexin-V staining (A), while proliferation rates were derived after assaying DNA content by PI staining (B). The anti-CD31 Moon-1 mAb was added to the coculture (10 μg/mL, replaced every 48 hours) to verify the specificity of the interaction. The anti–HIV-1 gp120 JAS mAb was used with similar modalities as the irrelevant control. Data are the mean values obtained using B-CLL cells from 4 patients in 2 separate experiments; error bars represent the SD.